In a number of applications, light-weight, high strength structural members are required. For example, in motor vehicles and aircraft as well as in various devices, such as home appliances and the like a number of composite materials have been proposed in the past as structural members, such as exotic light-weight alloys. In most applications, however, mass reduction must be balanced against the cost of the product to the consumer. Thus, there is a need for providing strength without significantly increasing material and labor costs. Moreover, reinforcement techniques are needed which can be adapted to existing geometries of structural parts obviating any requirement for fundamental design changes.
It would be desirable to provide a structural member which may be generally considered as a wall with some form of reinforcement. While such forms of reinforcement could have numerous applications, it would be particularly desirable to provide such reinforcements for door panels of vehicles.
A typical motor vehicle door includes an outer skin or panel of thin steel or aluminum. The outer panel is attached to structural members and, along with an inner door panel, defines a space or cavity into which a movable window retracts. In addition to the movable window a number of latch fixtures and window actuators are located in this door space.
Due to the area of the outer panel and its thickness a phenomenon as xe2x80x9coil-canningxe2x80x9d may occur. The term oil-canning refers to oil cans of the type in which the bottom of the can flexes back and forth to dispense oil. This movement often creates a popping noise as the metal flexes. As applied to an outer door panel, oil-canning refers to the tendency of the door panel to flex from its desired position (often typically bowed) to a second, undesired position in which the outer panel is deformed or flexed inwardly toward the inner door panel. This movement may occur in response to slight pressures on the outer panel such as the weight of an individual leaning against the vehicle.
Although the oil-canning may be momentary with the panel immediately returning to its original configuration, it may be permanent and, moreover, may cause a crease to form in the panel coating. As will be understood by those in the art creases of this kind must be removed in a bump shop or the like and require that the panel be repainted.
While a number of side impact beams are known, these beams focus on the structural integrity of the motor vehicle in a crash and are not directed to the oil-canning problem. For example, a side impact beam for a vehicle door has been proposed which comprises an open channel-shaped metal member having a longitudinal cavity which is filled with a thermoset or thermoplastic resin-based material core. The core is disposed in the midspan of the beam. The core does not adhere to the sides of the beam. The core may include hollow glass microspheres in order to decrease density and thus weight.
Although filling large volumes of a door cavity could prevent oil-canning, such an approach would also significantly increase mass and thus weight, which, of course is an undesirable feature. In addition, large volumes of foam contribute significantly to cost. Finally, a large foam core often creates an unwanted heat sink. And, although increasing the metal gauge of the door panel or adding localized thick metal reinforcements will increase stiffness, as the metal thickness increases weight increases.
Accordingly, there is a need for a lightweight door panel stiffener which is economical to produce and install. Such stiffener is desirable for door panels in general even when not intended to address the oil canning phenomenon.
An object of this invention is to provide a reinforcement for a substrate or wall.
A further object of this invention is to provide such a reinforcement which has particular utility where the substrate or wall is a vehicle door panel.
In accordance with this invention a foiled backed laminate reinforcement for a wall or substrate is made from a sheet polymer bonded to a foil support. The polymer is preferably an expandable polymer foam which would be disposed,against the inner surface of the wall or substrate. Upon expansion of the polymer, the polymer foam material is bonded to the inner surface of the substrate.
In one aspect the present invention provides a foil/foam laminate reinforcement which prevents. or substantially reduces oil-canning of outer door panels. The foil/foam laminate has a thin layer of foil bonded to a layer of unexpended expandable resin. The foil/foam laminate is corrugated along its length. The resin side of the laminate is bonded to the inner surface of the outer door panel in approximately the center of the panel. Fixtures may be used to hold the laminate in place. As the motor vehicle moves through a, paint oven the resin expands through activation of a blowing agent and bonds more uniformly to the inner door surface. In one aspect valleys in the contact surface of the resin layer are filled in by the action of the foam expansion. The door panel reinforcement significantly. increases the stiffness of the door panel and eliminates or reduces the tendency of the panel to oil can.
In another aspect the present invention provide a method of reinforcing a door structure to reduce oil-canning. A foil/foam laminate reinforcement is provided which has a thin layer of foil bonded to a layer of unexpanded expandable resin. As stated the foil/foam laminate is corrugated along its length. The laminate is secured to the inner surface of the outer door panel in approximately the center of the panel by placing the resin side in contact with the inner surface of the panel. Fixtures may be used to hold the laminate in place. In one practice of the invention the resin is heated as the motor vehicle oven through a paint oven, which expands the resin through activation of a blowing agent. The expansion serves to bond the laminate more uniformly and securely to the inner door surface. As stated, the door panel reinforcement significantly increases the stiffness of the door panel and eliminates or reduces the tendency of the panel to oil can.